She added that his acid attack trial and subsequent imprisonment had been a “difficult and trying time for him”.

District Judge Robert Hunter committed Collins’ case to Woolwich Crown Court for sentencing on a date to be fixed.

Prosecutor Samantha Mitchell told the court on Wednesday: “The items… were found inside a crutch that was being used by Collins on September 10.

“Security officers were in the process of searching the cell occupied solely by Collins.

“He had been using the crutch because of an ankle injury.

“An officer removed a bottom rubber stopper and discovered the items.

“They contain evidence of messages and calls between Collins and his family.”

Collins hurled the corrosive substance over a crowd on the dance floor at the nightclub.

It left 16 people with chemical burns and three people temporarily blinded, one of whom still suffers from blurred vision in one eye.

He told his trial at Wood Green Crown Court he did not know the bottle contained acid, believing it to contain a liquid date rape drug, which he had snatched from two men after overhearing them planning to spike a girl’s drink.

But the jury convicted him of five counts of grievous bodily harm with intent and nine counts of actual bodily harm.

Trial Judge Noel Lucas ordered that, as well as his prison term, Collins, originally of Broxbourne, Hertfordshire, will additionally be subject to five further years on extended licence.